Rotary shear pin drive



Oct. 30, 1945. R. A. ROWSEY ROTARY SHEAR PIN DRIVE Filed Jun 27 1942 3 Sheets-Sheet 1 m w m Oct. 30, 1945. R. A. ROWSEY 2,388,186

ROTARY SHEAR PIN DRIVE Filed June 27, 1942 3 Sheets-Sheet 2 6 05 527 4. Eon/5E:

Oct. 30, 1945. R A RQWSEY 2,388,186

- ROTARY SHEAR PIN DRIVE Filed June 27, 1942 5 Sheets-Sheet 3 61's ##orney.

Patented Oct. 30, 1945 UNITED STATES PATENT OFFICE ROTARY snmn PIN DRIVE Robert A. RowsenGary, Ind.

. Application June 2'], 1942, Serial No. 448,784

(Cl. lie-28) zClaims.

This invention is a rotary shear pin drive which interrupts the transmission of rotary power when an exactly predeterminable overload occurs and can thereafter run freely for prolonged peri ods without damage, and which can be used with complete satisfaction under excentric loading conditions such as occur, for instance, when it is used in conjunction with a flexible coupling between misaligned shafts. Other advantages will become apparent from the following disclosure of 1 specific examples of the invention illustrated by than about .001 of an inch in the case oi the drive illustrated, this being sufllciently close spacing in view of the other dimensions to relieve the pin a 8 from all flexing stress, the pin and the sockets Figure 8, a section from the line V1IIVIII in Figure "I Figure 9, a section similar to Figures 2 and 4 but showing a third example; and

Figure 10, a partial end view of Figure 9.

More specifically, in the case of the first example the drive includes a Journal i and a bearing 2 in coacting relation which are mutually rigid to radial and longitudinal motions and which respectively have rigid radial mounts I and l providing mutually opp sed faces 6 and 8 in which registered shear pin sockets I and 8 are formed which are fitted with a shear pin 0. The faces 5 and i are machined precisely parallel and are so closely spaced while the sockets l and I encompass the pin I so closely that this pin works substantially entirely in pure shear without nexure, this meaning that the pin may be designed with an exactly predetermined strength in pure shear so as to cleanly shear and interrupt its ro-- tary transmission of power upon an exactly predeterminable overload, it being impossible for the pin to be stressed in any other manner than pure shear. The close spacing between the faces 5 and 6 is maintained by a thrust bearing formed by a plate ll screwed. to the journal I with an overhanging flange bearing against the outer end of the bearing 2, the sliding areas being amply large for their purpose. The arrangement is I and I being precision fits so that pin play is im- Possible.

Antifriction means in the form of a bearing liner H made of antifriction material, works between the journal I and the bearing 2 to form a heavy duty bearing assembly permitting prolonged free running upon shearing of the pin 9 due to the transmission of an overload through the drive. This means that the drive may be used at unattended places with complete safety, since there'ls no danger of a driving connection being reestablished alter pin shearing even though the parts run free for a prolonged time. When running free the bearing thrust is diminished to a point eliminating the need for the use of antifriction means in conjunction with the thrust hearing when the drive is not of too great size.

It is to be understood that to provide the radial and longitudinal rigidity to the Journal and hearing so as to preserve these characteristics at the shear pin location, the journal and bearing, including the thrust hearing, are a precision assembly. This is important since it permits the working of the pin 9 in pure shear without i'lexure regardless oi excentric loading oi either the Journal I or the bearing 2, the entire device being a rigid, unitary drive entirely free item looseness in any direction until the shear pin 8 is sheared, the action on the shear pin being analogous to a precision bar or rod shear resulting in the pin I being cleanly cut as contrasted to being fractured.

such that the faces I and I cannot separate more as The cut races of a sheared pin are smooth and entirely tree from the crystalline appearance of a fractured pin. As explained, this eiiect prevails regardless of excentric loading oi the drive because oi the drive being a completely rigid unit with no single part movable in any direction capable oi placing any load on the pin 9 other than pure shear.

With the foregoing in mind, the drive is shown as a part of a sprocket chain drive working a cantilever shaft driving a shear-oi a type intermittently loading this shaft so that it is intermittently loaded as a cantilever producing its deflection and eccentrically loading the described shear pin drive in a manner that is not ordinarily considered tolerable in the case of any prior art shear pin drive. More specifically, the journal i is provided with a bore ii in which is keyed this cantilever shaft I! while the outer periphery oi the bearing 2 mounts the sprocket II. the illustratlon showing the sprocket integral with the bearing since the illustrated drive was designed for thi application. Regardless of deflection of the shaft [3, the drive is a unit and, therefore. deflects in its entirety as a unit without flexure of the pin 9, the latter remaining in pure shear while working. Obviously no tension can possibly be transmitted to the pin 9 nor can it be subjected to vibration fatigue, the interruption of the rotary drive depending solely on the pure shear strength of the pin 9. It is to be understood that the metallurgical and mechanical designing arts are perfectly capable of producing the shear pin 9 with an arcuately predetermined shear strength, but these arts cannot hope to.

predict shear pin failure when the pin is subiected to a combination of shear, fiexure, tension. vibration fatigue, etc., as it is in the case of comparable prior art shear pin drives.

The mounts 3 and 4 take the form of circular discs with the sockets l and 8 used in multiple as slots which radially open outwardly, this permitting the drive to function as an indexing device by the removal and replacement of the shear pin in the sockets as required. but, at the same time, introducing the temptation to use more than one shear pin. This practice is entirely avoided by providing one of the mounts with an odd number of shear pin sockets and providing the other mount with an even number of shear pin sockets, this making it impossible to use more than one shear pin at a time and assuring the effectiveness of the drive for the purpose of enabling it to interrupt the transmissiomoi power upon a predetermined overload. It is, of course, possible to use the same number oi sockets for each of the mounts in the event it is desired to provide a drive that can meet varying conditions, since this will permit the use 01 more than one shear pin to adjust the load transmitting ability.

To definitely assure the desired shear action. the respective junctions between the faces I and I and the socket; l and 8 provide sharp cutting corners, the mounts providing the metal torming these corners and the bounding surfaces of the shear pin sockets being made or hardenable metal and being hardened in the manner of true shear knife elements, the shear pin 9 being preferably made or metal that is relatively softer than that described so that the shear pin sockets and shear pin that might be jammed. Thi is desirable because the shear pins must flt the sockets with such precision as to possibly make shear pin removal diflicult particularly after prolonged use of a pin. A second ring it is fixed to the periphcry of the mount I by screws l8 working through arcuate slots 20 in thi ring ii, the latter having a flange 2| that radially closes the sockets 8 in the periphery of the mount I against shear pin displacement and this flange having slots 22 which register with the sockets 8 when the ring is is turned upon loosening of the screws l9 whereby to both radially and longitudinally open the socket 8 for shear pin removal. When the ring i8 is turned to close the slots 8, shear pin displacement is positively prevented, it being understood that the holes H in the ring I! are smaller than the lateral dimensions or the pin. Since the rings l5 and I8 are entirely separated, they cannot possibly interconnect the two mounts either frictionally or otherwise, this adding to the precision of the device since all the load must be carried by the pin 9 in pure shear. At the same time, partial radial displacement of the shear pin is positively prevented so that it cannot recede from the axis or the drive to permit the shear pin to carry a greater load than that for which it was calculated.

Going now to the second example, a drive is shown incorporated with a flexible coupling interconnecting misaligned shafts, this application being one where the prior art shear pin drives cannot be applied because of the heavy eccentric loading applied the drive by the working of the flexible coupling necessary to accommodate the misalignment. In this example the journal 23 has a bore 24 and is keyedto one of the misaligned shai'ts 28, the cooperating bearing 28 having a bore 21 in which the outer races of tapered 0 roller bearing assemblies 28 are tightly inserted.

their corners cannot wear out of shape and introduce loosenesg which would eliminate the eftectiveness oi the action described. Precise machining is necessary, it being necessary to cut the sockets in the mounts prior to their hardening. and to accurately grind them to precise size after hardening. the shear pins used being, of course, accurately ground to precise size to exactlyfltthe sockets. 'rheexactshapesorthe socketslmdtbeshearpinsarelmmaterialprovidlng it is such as permits precision fitting oi the shear pins in the sockets without looseness 0! any sort and without causing the transmission totheshcarpinoianystreasotherthanpurc To prevent shear Pin displacement during the operation 0! the drive, a ring II is permanently flxedtotheperipheryoithemmmttthisring providing a flange Ii that overhangs the sockets lsoostoradiallyclosethesameagainstshear pin displacement. This ring II is provided with holes II which register with the sockets I in axlalalignmentsothatashearplndrlvingtool the inner races oi these assemblies tightly encircling the journal 23. The arrangement follows precision tapered roller bearing arrangements, the bore 21 in the bearing 20 providing an inward flange 28 against which the outer race of the inside one of the assemblies 28 rigidly rests, the other outer race being rigidly held in the bore against the one resting against the flange 19 by a retainer ring screwed to the outside end of the bearing 28; the inner race of the inside one of the assemblies resting agalnstanannular ring 3| surrounding the journal 28 and bearing against its shear pin socket mount II, which takes the form of a rigid circular plate like the plate 3 oi the first example, while the inner race of the outside one or the assemblies 2! is rigidly held on the journal 23 against the first mentioned inner race by a retainer plate I! screwed to the end of the Journal 23. Assuming commercially obtainable precision tapered roller bearing assemblies are used, it is obvious that the Journal 23 and the bearing 26 are completely rigid to both radial motion and longitudinal motion in any direction, while being extremely free to rotary motion, said assemblies providing a combined radial and thrust bearing.

As in the case of the first example, the mounts 32 and II provide opposed precisely ground parallel faces 34 and II, respectively, each having a. circumferential series or shear pin sockets I! and I! in which a shear pin I8 is fitted, the arrangements being exactly as described before regarding the necessity for precision fitting or the various parts. The ring ll provides a means for may be used through these holes to dislodge a 16 positively spacing the faces and It the disessence tance found to most effectively assure precision shearing of the shear pin while permitting free running after the pin shears, .001 of an inch having been found satisfactory for this purpose in most instances. However, since the drive now being described can be made with extreme precision, this space can be still further reduced to a point where actual contact between the faces 34 and 35 almost, but not quite, occurs. A somewhat diflerent arrangement prevents shear pin displacement in this instance, it consisting of a split ring is screwed to the outside of the mount 81 and fashioned to completely close the shear pin sockets. Such an arrangement is not so feasible in the case of prior art shear pin drives because in those instances shear pin breakages frequently occur regardless of an overload, whereas in the present instance the only way the shear pin can fail is by being placed in sufllcient pure shear stress to cut cleanly through and this can only occur by reason of an overload.

The outside of the bearing 28 provides the dogs I which cooperate with the free dog plate 4| cooperating with the other dog plate 02 necessary to complete the flexible coupling, it being the dog plate 42 that is flxed by a key 43 to the other misaligned shaft 44. Regardless of lubrication. such a flexible coupling tends to eccentrically load the parts with which it is associated in a more or less unpredictable manner, this being immaterial in the case of the present shear pin drive because it constitutes a unitary assembly the individual parts of which are rigidly associated against all movements other than pure rotation which is restrained by the shear pin, whereby everything wdrks as a unit.

Here again, the mounts 32 and 33 should be made or heat treated hardenable material, preferably steel, this particularly including the shear pin socket parts. The ring 3| should also be made of hardened material, such as heat treated steel, the use of this ring being advantageous since it permits grinding of the faces 34 and 35 to practice parallelism after heat treatment of the mounts, the ring 3| then being parallel ground to dimensions properly spacing these faces. Tapered roller bearing assemblies are inherently free oi radial or longitudinal looseness caused by wear when installed in the manner disclosed, and, naturally, the drive may run free indefinitely after shearing of the pin ll so that it is unnecessary to have an attendant watching the equipment it protects. In accordance with good machine practice. all parts subjected to deformation should be made of hardened metal. Naturally, the flexible coupling elements should also be hardened as by heat treating the proper grade of steel.

In the case of the third example, the Journal .05 is keyed to a cantilever shaft 18, the bearing l1 constituting the pulley of a heavy-duty V-belt drive and having a series of circumferential grooves II for this purpose, the inside of the bearing l1 providing a bore 48 in which heavy-duty tapered roller bearing assemblies 50 are positioned. The outer races of these assemblies rigidly rest against an inward flange ii at the in the case of the ring II in the second example. A further refinement is the use of a lubricatins duct 80 leading from the outside 0. the bearing where it is plugged by a suitable iiush screw which can be removed to: substitution by an industrial grease fitting, to the inside of the bore 4! to the heavy duty tapered roller bearing assemblies, a lubricant seal 51 between the outer ends of the journal and the bearing preventing lubricant loss. These refinements are necessary because the drive now being disclosed is intended for extremely heavy duty.

In the case of the other two examples, the shear pin socket mounts are integral parts of the Journal and bearing respectively. This requires them being made of hardenable material and their being heat treated throughout, a practice that becomes rather expensive in the case of a large part such as is involved by the bearing of the third example. Therefore, in this instance, the mount 58 which rigidly extends radially from the journal it constitutes a hat circular hardened plate that is a part of the Journal end, but the other mount that is rigidly carried by the hearing 41 takes form of an annular hardened plate that is rigidly screwed to the journal end, so that only the shear part 59 need no heat treated, these plates providing the ground parallel 1mished races 00 and BI, and the shear pin sockets 62 and. whic carry the shear pin 64. The shear pin retainer takes the form 01' an inwardly flanged cylindrical ring 66 that is axially fitted and screwed into place, this ring being solid. It

' is to be understood that here again the faces 60 end of the bearing bore 49, the holding force being provided by a retainer ring 02 rigidly screwed to the other end of the bearing, the inner races being iorced against an outward flange 51 at the inside and SI should be ground precisely parallel with a separation not greatly exceeding .001 of an inch, while the shear pin sockets and the pin itself are ground to precision fits, all for reasons already described. Also, the shear pin sockets 62 and 63 are formed as circumferential series about the outer edges of the two mounts formed by the plates iii and 5!, but in this instance the sockets are made with diiferent sizes to accommodate shear pins having diii'erent dimensions, whereby the load transmitting ability of the device may be varied. Since the shear pin works in pure shear, it may have extremely small dimensions while carrying a relatively heavy load, it being remembered that the pin is not called upon to work as a beam or as a tensioned device. In all events, the dimensions of the shear pin depend upon the shearing action exerted by the true, sharp shearing parts of the drive, this -action being increased when the drive must carry shock loads and being materially decreased in the case of steady loads. Furthermore, in all instances a smaller pin may be used than in prior art devices, since it is relieved of all loading excepting pure shear.

This is a continuatlon-in-part of my copending application flled April 10, 1940, and bearing Serial No. 328,979.

I claim:

1. A rotary power drive including spaced c0- axlal rotary plates with atleast one shear pin socket in each of their peripheral portions and a shear pin in said sockets and coupling said plates, the latter being positively spaced closely together and providing clean cutting shearing surfaces for said pin, said sockets comprisim radially open recesses in the peripheries of said plates with one 01' said plates provided with a permanent part radially closing its said slot and having an opening registering with the end of said pin for lasertion of a driving tool, the other of said plates havin: a closure for radially closing its said slot which can be opened to permit removal of said pin.

2. A rotary power drive comprising a first rotary plate of circular contour having a hollow shaft for keying to a shaft passed therethrough, a second rotary plate of circular contour having the same diameter as that of said first plate and journaied on said hollow shaft for free rotation, means for positively holding the opposed faces of said plates in closely spaced relation, a plurality of radially open slots formed in the peripheries of said plates parallel the axes of the latter, at least one shear pin inserted in registered ones of said slots of the respective plates, a permanent radial closure for the slots on one of said plates with holes registered with said slots for passage of a shear pin driving tool to permit said pin being driven longitudinally to eflect its removal, a rotary member for radially closing the slots of the other of said plates and for closing the ends thereof remote from the other of said plates and having openings that register with said slots by rotating said member so said shear pin can be radially or longitudinally removed from its slot, releasable means for fixing said member against rotation respecting the plate having the slots closed thereby and means efiectlng rotary power connection with said second plate.

ROBERT A. ROWSE'Y.

CERTIFI CA TE OF CO RREC TI ON Patent No. 2,588, 86.

October 50; 19l 5.

ROBERT A ROWSEY It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, first column, line 15, for "arcuately" read --accurately--; page 5, first column, line lg-Ld for "practice" read --precise--; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 12th day 01 February, A. D. l9l 6.

(Seal) Leslie Frazer First Assistant Commissioner of Patents.

in: a closure for radially closing its said slot which can be opened to permit removal of said pin.

2. A rotary power drive comprising a first rotary plate of circular contour having a hollow shaft for keying to a shaft passed therethrough, a second rotary plate of circular contour having the same diameter as that of said first plate and journaied on said hollow shaft for free rotation, means for positively holding the opposed faces of said plates in closely spaced relation, a plurality of radially open slots formed in the peripheries of said plates parallel the axes of the latter, at least one shear pin inserted in registered ones of said slots of the respective plates, a permanent radial closure for the slots on one of said plates with holes registered with said slots for passage of a shear pin driving tool to permit said pin being driven longitudinally to eflect its removal, a rotary member for radially closing the slots of the other of said plates and for closing the ends thereof remote from the other of said plates and having openings that register with said slots by rotating said member so said shear pin can be radially or longitudinally removed from its slot, releasable means for fixing said member against rotation respecting the plate having the slots closed thereby and means efiectlng rotary power connection with said second plate.

ROBERT A. ROWSE'Y.

CERTIFI CA TE OF CO RREC TI ON Patent No. 2,588, 86.

October 50; 19l 5.

ROBERT A ROWSEY It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, first column, line 15, for "arcuately" read --accurately--; page 5, first column, line lg-Ld for "practice" read --precise--; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 12th day 01 February, A. D. l9l 6.

(Seal) Leslie Frazer First Assistant Commissioner of Patents. 

